This invention relates to a final drive suspension system for a vehicle.
Final drives have been provided in motor vehicles for transmitting the drive from a cardan shaft to an axle shaft having driving wheels secured thereon. The final drive has a bevel pinion integral with a drive shaft coupled through a cardan joint to the cardan shaft. The bevel pinion meshes with a bevel wheel for turning the drive round through 90 degrees and reducing the drive in speed. During vehicle driving, the final drive is subject to torques of reaction around the axis of the cardan shaft (cardan shaft moment) and also around axis of the axle shaft (starting moment). For this reason, the final drive should be suspended elastically at the floor or the vehicle in order to reduce vibrations and noises which would be transmitted to the vehicle if it is mounted rigidity at the floor of the vehicle. However, it is impossible to nullify final drive motions merely by elastically suspending the final drive at the floor of the vehicle.
Various approaches have been proposed to reduce vibrations transmitted from the final drive to the cardan shaft. For example, U.S. Pat. No. 4,699,230 describes an axle gear casing suspension system for elastically flexibly suspending a rear axle gear casing at least two suspension points. One of the suspension points is shifted from a torque support plane determined by the other suspension point so that swivel motions of the same magnitude are produced in opposite directions at a connection point between the cardan shaft and the drive shaft. This is effective to reduce changes in the position of the connection point which is subject to the influence of the starting and cardan shaft moments.
With such a conventional suspension system, however, it is impossible to hold the drive shaft in its original position under the influence of the starting and cardan shaft moments. Particularly when a universal joint, such as cardan joint, is used to couple the cardan joint to the drive shaft, a secondary moment, which corresponds to the joint angle between the cardan shaft and the drive shaft, will occur to produce vibrations and noises. The vibrations and noises will increase as the angle of the drive shaft with respect to the cardan shaft changes because of changes in the position of the final drive.